Method for tracing the flow of water in subterranean formations



United States Patent 3,508,875 METHOD FOR TRACING THE FLOW OF WATER IN SUBTERRANEAN FORMATIONS Burton B. Sandiford, Placentia, Calif., assignor to Union Oil Company of California, Los Angeles, Calif., a corporation of California No Drawing. Filed Oct. 3, 1967, Ser. No. 672,448 Int. Cl. G01n 31/22, 33/24; E21b 47/10 US. Cl. 23230 6 Claims ABSTRACT OF THE DISCLOSURE A method for tracing the flow of water from a plurality of origin points to at least one recovery point in which a difierent water-soluble iodide, thiocyanate or salicylate compound is added to the water at each origin point and the recovered Water analyzed for the presence of iodide, thiocyanate and salicylate by admixing a portion of the recovered water with carbon tetrachloride and then adding ferric chloride solution.

This invention relates to the study of water flow and more particularly is concerned with a method for tracing the flow of water in subterranean formations.

It is often desired to ascertain the flow pattern of Water through porous subterranean formations, such as petroleum reservoirs. Methods for tracing the flow of water in subterranean areas are useful in the oil well treating field and are especially useful in tracing the flow of an aqueous flooding medium through an oil-bearing formation as from an input to an output Well. Accordingly, it has been suggested that various agents be added to the water at an injection point and that a sample of the Water withdrawn at a remote point be analyzed for the presence of the tracer material to indicate the passage of the water from the injection point to the recovery point.

In the typical petroleum recovery operation, an aqueous drive fluid is injected into the formation through a plurality of injection wells and formation fluids recovered through one or more spaced production wells. The input and production wells can be arranged in any convenient pattern, the location of existing wells often determining the arrangement of wells employed in secondary recovery operations. In these complex flow systems wherein a flooding medium is injected through a plurality of input wells and fluids recovered from one or more production wells, it is necessary that a different tracer material be employed in each injection well to be tested so that the source of water withdrawn from a production well can be identified. Thus, in the case where three input wells are employed, it is necessary that a different tracer be injected into each of the injection wells and that the water Withdrawn from each of the injection wells be separately analyzed for each of the tracer materials. It is readily apparent that such testing is undesirably time consuming, particularly where a number of production wells must be tested for the presence of tracer.

Accordingly, a principal object of the present invention is to provide a method for tracing the flow of Water from a plurality of origin points. Another object of the invention is to provide a method for studying the flow of aqueous media in a complex flow system wherein the aqueous media originates from a plurality of source points. Still another object is to provide a simple test for analyzing samples of water for the presence of up to three selected tracer materials. Other objects and advantages of the invention will be obvious to those skilled in the art from the following more detailed description.

In accordance with the method of the present invention for tracing the flow of Water in subterranean formations,

a different distinctive tracer is added to the water at each of up to three origin points and portions of the water obtained at a recovery point analyzed for the presence of the tracer materials to indicate derivation or flow from the origin points. Since different tracers are added to the water at each of the origin points, the source of the Water obtained at the recovery point is readily ascertained because of the distinctive reaction of the tracer materials. The tracer materials useful in the practice of this invention and which can be readily identified by a simple qualitative test are water-soluble iodides, thiocyanates and salicylates.

Various water-soluble iodide salts, such as the alkali metal iodides and in particular, sodium and potassium iodide, have heretofore been proposed as tracers useful in studying the fiow of Water through subterranean earth formations. The iodide salt, or an aqueous iodide solution, is added to the water at an origin point, such as a water injection well, and the Water at the recoverye well analyzed for the presence of iodide. In the practice of this invention, water-soluble iodide can be employed as a tracer by the addition of this material at one of the origin points in accordance with conventional practice.

The use of Water-soluble thiocyanate as a tracer is particularly described in US. Patent No. 3,003,856. In accordance with this method, a water-soluble thiocyanate ion yielding compound is added to the water at an origin point and the water at the recovery point analyzed for thiocyanate ion to indicate derivation from the origin point. Water-soluble thiocyanate yielding compounds useful in the practice of this invention include ammonium thiocyanate and the thiocyanates of an alkali metal, e.g. with an atomic weight of 22 to 40, i.e. sodium and potassium. In the practice of the present invention, water-soluble thiocyanate can be employed as a tracer by the addition of this material at one of the origin points in accordance with the patented method.

Water-soluble salicylate is another material particularly useful as a tracer in studying water flow. A method employing this material is described in a patent application by John A. Gurney filed concurrently With the instant application. In accordance with this method, the ammonium and alkali metal salts of salicyclic acid, e.g. the sodium and potassium salts are particularly preferred. In the practice of the instant invention, water-soluble salicylate can be employed as a tracer by the addition of this material at one of the origin points.

Thus, in accordance with this invention, the flow of water or other aqueous media originating at up to three origin points can be studied by simultaneously adding a different tracer material at each of the origin points and analyzing the water obtained from at least one recovery point for the presence of tracer. The source of water can be identified by the presence of tracer in the recovered water. In one application of this invention, a different tracer can be injected into each of up to three injection wells and the source of Water recovered at various production wells determined by detecting the presence of tracer material in the recovered water.

Whereas it has heretofore been necessary to run as many as three different tests on each water sample to detect the presence of tracer material, it is now possible in accordance with the method of this invention to detect the presence of iodide, thiocyanate and salicylate by a single simple analytical procedure. A sample of water can be analyzed for the presence of these compounds at relatively low concentrations, such as at concentrations of as low as 5 or 10 ppm, by admixing a small quantity of the water to be tested with a small amount of carbon tetrachloride and then adding ferric chloride solution. The carbon tetrachloride is substantially immiscible with the water and separate aqueous and nonaqueous liquid phases are formed. The color of each of these phases is characteristic of the particular tracer materials present in solution. A violet color in the carbon tetrachloride phase indicates the presence of iodide. Thiocyanate is indicated by the water phase being colored red and salicylate by a violet to purple color in the Water phase.

In one particular test procedure, about 4 ml. of carbon tetrachloride is admixed with about 5 ml. of the recovered water in a small via and the liquid contents mixed by vigorously shaking the vial. About 5 drops of acidic ferric chloride solution is then added to this mixture and the colors of the resulting liquid phases observed. The ferric chloride solution is prepared by admixing about 90 parts of saturated aqueous ferric chloride solution with about parts of hydrochloric acid.

EXAMPLE I The flow of water in a subterranean oil reservoir subjected to a water flooding operation is studied to determine the source of the Water recovered at the producing well. Injection wells A, B and C are arranged in a roughly triangular pattern and the production well is substantially centrally located intermediate the injection wells. Aqueous potassium iodide is injected into well A, aqueous ammonium thioeyanate into well B and aqueous sodium salicylate solution into well C. The Water recovered from the production wells is tested for the presence of tracer materials by admixing 5 ml. of the produced water with about 4 ml. of carbon tetrachloride and then adding about 5 drops of acidic ferric chloride solution. Within 24 hours after injection of the tracer materials, salicylate was detected in the produced water as evidenced by a purple coloration in the Water phase of the test mixture. The rapid passage of the tracer through the formation indicates a substantially open and unrestricted flow channel communicating Well C and the producing well.

While one application of this invention has been described, it will be apparent that the invention can be employed in other applications, such as for instance tracing the possible contamination of water in water Wells and determining the rate of flow of liquid from one well to another. Further, various modifications and changes can be made in the practice of the invention without departing from the scope and spirit of the invention.

Having now described the invention, I claim:

1. A method for tracing the flow of water from a plurality of origin points, which comprises:

adding a different tracer selected from the group consisting of water-soluble iodides, water-soluble thiocyanates and water-soluble salicylates to each of up to three origin points;

recovering a sample of water at a recovery point; and

admixing a small amount of said sample with carbon tetrachloride and thereafter adding ferric chloride solution to detect the presence of iodide, thiocyanate or salicylate indicating water derivation from an origin point.

2. A method for tracing the flow of an aqueous media 0 through a subterranean petroleum reservoir from a plurality of input wells to an output well, which comprises:

adding a water-soluble iodide to a first injection well;

adding a water-soluble thiocyanate to a second injection well;

adding a water-soluble salicylate to a third injection well;

recovering water from the output well; and

admixing a small portion of the recovered water with carbon tetrachloride and thereafter adding acidic ferric chloride solution to detect the presence of iodide, thiocyanate or salicylate indicating water derivation from an origin point.

3. The method defined in claim 2 wherein said iodide compound is potassium iodide.

4. The method defined in claim 2 wherein said thiocyanate is ammonium thiocyanate.

5. The method defined in claim 2 wherein said salicylate is sodium salicylate.

6. The method defined in claim 2 wherein said acidic ferric chloride consists of about parts of aqueous saturated ferric chloride solution and about 10 parts hydrochloric acid.

References Cited UNITED STATES PATENTS 2,553,900 5/1951 Doan et al. 3,003,856 10/1961 Boyd.

FOREIGN PATENTS 8/1964 Canada.

OTHER REFERENCES MORRIS O. WOLK, Primary Examiner R. M. REESE, Assistant Examiner US. Cl. X.R. 166-552 

